Not Applicable
This invention relates to a micro-electromechanical assembly. More particularly, this invention relates to a micro-electromechanical assembly which incorporates a covering formation for a micro-electromechanical device.
The following patents/patent applications are incorporated by reference.
As set out in the above referenced applications/patents, the Applicant has spent a substantial amount of time and effort in developing printheads that incorporate micro electromechanical system (MEMS)xe2x80x94based components to achieve the ejection of ink necessary for printing.
As a result of the Applicant""s research and development, the Applicant has been able to develop printheads having one or more printhead chips that together incorporate up to 84 000 nozzle arrangements. The Applicant has also developed suitable processor technology that is capable of controlling operation of such printheads. In particular, the processor technology and the printheads are capable of cooperating to generate resolutions of 1600 dpi and higher in some cases. Examples of suitable processor technology are provided in the above referenced patent applications/patents.
The Applicant has overcome substantial difficulties in achieving the necessary ink flow and ink drop separation within the ink jet printheads. A number of printhead chips that the Applicant has developed incorporate nozzle arrangements that each have a nozzle chamber with an ink ejection member positioned in the nozzle chamber. The ink ejection member is then displaceable within the nozzle chamber to eject ink from the nozzle chamber.
A particular difficulty that the Applicant addresses in the present invention is to do with the delicate nature of the various components that comprise each nozzle arrangement of the printhead chip. In the above referenced matters, the various components are often exposed as a requirement of their function. On the MEMS scale, the various components are well suited for their particular tasks and the Applicant has found them to be suitably robust.
However, on a macroscopic scale, the various components can easily be damaged by such factors as handling and ingress of microscopic detritus. This microscopic detritus can take the form of paper dust.
It is therefore desirable that a means be provided whereby the components are protected. Applicant has found, however, that it is difficult to fabricate a suitable covering for the components while still achieving a transfer of force to an ink-ejecting component and efficient sealing of a nozzle chamber.
The Applicant has conceived this invention in order to address these difficulties.
According to a first aspect of the invention, there is provides a micro-electromechanical assembly that comprises
a substrate that incorporates drive circuitry;
a micro-electromechanical device that is positioned on the substrate and is electrically connected to the drive circuitry to be driven by electrical signals generated by the drive circuitry; and
a covering formation that is positioned on the substrate and is configured to enclose the micro-electromechanical device.
The covering formation may include sidewalls that extend from the substrate and a roof wall that spans the substrate.
The micro-electromechanical device may include an elongate actuator that has a fixed end that is connected to the substrate so that the actuator can receive an electrical signal from the drive circuitry and a movable end, the actuator being configured so that the movable end is displaced relative to the substrate on receipt of the electrical signal.
A motion-transmitting structure may be fast with the movable end of the actuator. The motion-transmitting structure may be connected to a working member so that movement of the actuator is translated to the working member. The motion-transmitting structure may define part of the roof wall and may be spaced from a remaining part of the roof wall to allow for movement of the motion-transmitting structure.
The roof wall may define a cover that spans the walls to cover the elongate actuator. The motion-transmitting structure may be shaped so that the cover and the motion-transmitting structure define generally co-planar surfaces that are spaced from, and generally parallel to the substrate. An opening may be defined between the cover and the motion-transmitting surface to facilitate relative displacement of the cover and the motion-transmitting surface.
The actuator may include at least one elongate actuator arm of a conductive material that is capable of thermal expansion to perform work. The actuator arm may have an active portion that defines a heating circuit that is connected to the drive circuitry layer to be resistively heated on receipt of the electrical signal from the drive circuitry layer and subsequently cooled on termination of the signal, and a passive portion which is insulated from the drive circuitry layer, the active and passive portions being positioned with respect to each other so that the arm experiences differential thermal expansion and contraction reciprocally to displace the movable end of the actuator.
The motion-transmitting structure may define a lever mechanism and may have a fulcrum formation that is fast with the substrate and pivotal with respect to the substrate and a lever arm formation mounted on the fulcrum formation. An effort formation may be connected between the movable end of the actuator and the lever arm formation and a load formation may be connected between the lever arm formation and the working member.
The lever arm formation, the cover and the walls may define a unitary structure with the lever arm formation being connected to the walls with a pair of opposed torsion formations that are configured to twist as the lever formation is displaced.
The sidewalls may include nozzle chamber walls, the roof wall defining a nozzle chamber together with the nozzle chamber walls and the motion-transmitting structure. The roof wall may define an ejection port in fluid communication with the nozzle chamber, the working member being in the form of a fluid ejection device that is positioned in the nozzle chamber, such that displacement of the working member results in ejection of fluid in the nozzle chamber from the ejection port. The substrate may define a fluid inlet channel in fluid communication with the nozzle chamber to supply the nozzle chamber with fluid.
According to a second aspect of the invention, there is provided a printhead chip for an inkjet printhead, the printhead chip comprising
a substrate; and
a plurality of nozzle arrangements that is positioned on the substrate, each nozzle arrangement comprising
nozzle chamber walls and a roof that define a nozzle chamber with the roof defining an ink ejection port in fluid communication with the nozzle chamber;
an ink-ejecting member that is positioned in the nozzle chamber, the ink-ejecting member being displaceable towards and away from the ink ejection port so that a resultant fluctuation in ink pressure within the nozzle chamber results in an ejection of ink from the ink ejection port;
at least one work-transmitting structure that is displaceable with respect to the substrate and is connected to the ink-ejecting member so that displacement of the work transmitting structure results in displacement of the ink-ejecting member;
an actuator that is connected to the work-transmitting structure, the actuator being capable of displacing the work transmitting structure upon receipt of an electrical drive signal; and
air chamber walls and a covering formation that is positioned over the actuator, the air chamber walls and the covering formation defining an air chamber in which the actuator is positioned, the roof, the work transmitting structure and the covering formation together defining a protective structure positioned in a common plane.
The invention is now described, by way of example, with reference to the accompanying drawings. The following description is not intended to limit the broad scope of the above summary.